1. Field of the Invention
The present invention relates generally to a communication apparatus and a control method thereof More particularly, the present invention relates to an apparatus for decoding a space-time block coded (STBC) signal and a control method thereof.
2. Description of the Related Art
Mobile communication systems are advancing to wireless data packet communication systems of high speed and high quality to provide data service and multimedia service over CDMA 2000 1x networks beyond voice oriented service provided over the conventional IS-95A and IS-95B networks. 3rd-generation (3G) mobile communication systems discussed as the wireless data packet communication systems comprise High Speed Downlink Packet Access (HSDPA) based on 3GPP and 1xEVDV system based on 3GPP2. The 3G mobile communication system enables to transmit radio packet data of high speed and high quality over 2 Mbps. Further, a 4G mobile communication system is under development to provide very high speed and high quality multimedia service over Internet Protocol (IP) network.
Since the high speed packet data service provides multimedia contents to a mobile terminal, a downlink capacity from a base station to the mobile terminal needs to increase. To increase the downlink capacity, more base stations can be installed or the frequency band can be extended. However, the base station installation requires much cost and the frequency band extension is subject to practical limitations. Instead, 3GPP/3GPP2 employs an array antenna to standardize a multiple antenna technique for enhancing the system throughput and the transmission capability of the base station.
The multiple antenna technique can provide transmit diversity and mitigate the multipath fading occurring in the downlink radio channel. Representative transmit diversity techniques comprise a Selective Transmit Diversity (STD), Space Time Spreading (STS), Space-Time Block Coding (STBC), and so forth. The transmit diversity techniques can be divided to an open-loop scheme which requires no feedback information and a closed-loop scheme which requires feedback information based on whether the feedback information including channel information is transmitted from a receiver to a transmitter.
The STD adopts the closed-loop scheme, and the STS and the STBC adopt the open-loop scheme. In general, the transmit diversity requiring the feedback information is subject to the degradation of the system throughput because of the transfer delay and the transfer error of the feedback information. Hence, it is difficult to apply the transmit diversity in a radio environment where the mobile terminal travels quite fast. The transmit diversity techniques can be classified to an antenna space technology. In the antenna space technology, the transmitter transmits signals over the individual transmit antenna and the receiver estimates the multipath fading channel from the individual transmit antenna and acquires a diversity gain by processing the signals received from the transmit antennas.
A representative adaptive antenna system using the antenna space technology is a Multiple Input Multiple Output (MIMO) system. Since the MIMO system spatial-multiplexes and transfers data, the communication system throughput can be greatly enhanced. On the assumption that the receiver can acquire the channel information, the MIMO system achieves a high data rate and a low bit error probability.
Particularly, a quasi-orthogonal STBC scheme is the transmission of transmission rate ‘1’. The receiver uses a maximum likelihood detection to decode the quasi-orthogonal STBC scheme. Disadvantageously, the maximum likelihood detection suffers high complexity.